The tube has two separated channels or lumens running down its length. One is open at both ends and drains urine into a collection bag. The other has a valve on the outside end and connects to a balloon at the tip. The balloon is inflated with sterile water when it lies inside the bladder to stop it from slipping out. Foley catheters are commonly made from silicone rubber or natural rubber.

A section cut of the distal end of a Foley Catheter. Shown in the image is a burst balloon, balloon lumen and main drain lumen

Foley catheters should be used only when indicated, as use increases the risk of catheter-associated urinary tract infection and other adverse effects.

Side view diagram of a three-way Foley catheter, in place for bladder irrigation and drainage. The balloon near the tip holds the catheter in place.

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In an emergency department, indwelling urinary catheters are most commonly used to assist people who cannot urinate.[1] Indications for using a catheter include providing relief when there is urinary retention, monitoring urine output for critically ill persons, managing urination during surgery, and providing end-of-life care.[1]

A Foley catheter can also be used to ripen the cervix during induction of labor. When used for this purpose, the procedure is called extra-amniotic saline infusion (EASI).[2] In this procedure, the balloon is inserted behind the cervical wall and inflated, such for example with 30 mL per hour.[2] The remaining length of the catheter is pulled slightly taut and taped to the inside of the woman's leg. The inflated balloon applies pressure to the cervix as the baby's head would prior to labor, causing it to dilate. As the cervix dilates over time, the catheter is readjusted to again be slightly taut and retaped to maintain pressure. When the cervix has dilated sufficiently, the catheter drops out.[3]

Indwelling urinary catheters should not be used to monitor stable people who are able to urinate or for the convenience of the patient or hospital staff.[1]

In the United States, catheter-associated urinary tract infection is the most common type of hospital-acquired infection.[1] Indwelling catheters should be avoided when there are alternatives, and when patients and caregivers discuss alternatives to indwelling urinary catheters with their physicians and nurses then sometimes an alternative may be found.[1] Emergency physicians can reduce their use of indwelling urinary catheters when they follow evidence-based guidelines for usage, such as those published by the Centers for Disease Control and Prevention.[1]

A major problem with Foley catheters is that they tend to contribute to urinary tract infections (UTI). This occurs because bacteria can travel up the catheter to the bladder, where the urine can become infected. To combat this, the industry is moving to antiseptic coated catheters. This has been helpful, but has not completely solved this major problem. An additional problem is that Foley catheters tend to become coated over time with a biofilm that can obstruct the drainage. This increases the amount of stagnant urine left in the bladder, which further contributes to the problem of urinary tract infections. When a Foley catheter becomes clogged, it must be flushed or replaced.

There are several risks in using a Foley catheter (or catheters generally), including:

The balloon can break as the healthcare provider inserts the catheter. In this case, the healthcare provider must remove all balloon fragments.

The balloon might not inflate after it is in place. In some institutions, the healthcare provider checks the balloon inflation before inserting the catheter into the urethra. If the balloon still does not inflate after placement into the bladder, it is discarded and replaced.

Urine stops flowing into the bag. The healthcare provider checks for correct positioning of the catheter and bag, or for obstruction of urine flow within the catheter tube.

Urine flow is blocked. The Foley catheter is discarded and replaced.

The urethra begins to bleed. The healthcare provider monitors the bleeding.

Catheterization introduces an infection into the bladder. The risk of bladder or urinary tract infection increases with the number of days the catheter is in place.

If the balloon is opened before the Foley catheter is completely inserted into the bladder, bleeding, damage and even rupture of the urethra can occur. In some individuals, long-term permanent scarring and strictures of the urethra could occur.[5]

Defective catheters may be supplied, which break in situ. The most common fractures occur near the distal end or at the balloon.

Catheters can be pulled out by patients while the balloon is still inflated, leading to major complications or even death. This may occur when patients are mentally impaired (e.g. they have Alzheimer's) or are in a mentally altered state (e.g. they are coming out of surgery).

The relative size of a Foley catheter is described using French units (F).[7] The most common sizes are 10 F to 28 F. 1 F is equivalent to 0.33 mm = .013" = 1/77" of diameter.

Foley catheters come in several types:

Coudé (French for elbowed) catheters have a 45° bend at the tip that facilitates easier passage through an enlarged prostate.

Councill tip catheters[8] have a small hole at the tip so they can be passed over a wire.

Three way, or triple lumen catheters have a third channel used to infuse sterile saline or another irrigating solution. These are used primarily after surgery on the bladder or prostate, to wash away blood and blood clots.